The three dimensional structure of chicken erythrocyte nucleosomes will be determined by X-ray crystallography. The goal of this research is to elucidate the molecular structure of the nucleosome in sufficient detail to significantly increase our understanding of events such as transcription, replication, cell division, factors controlling certain aspects of gene regulation at the nucleosomal level. The structure should permit us to understand the detailed manner in which DNA is coiled around the histone core of the nucleosome. Careful interpretation of the structure should also provide new details concerning nucleosome-nucleosome interactions, nucleosome assembly, the changes in DNA packaging which presumably occur during replication and transcription, histone-histone interactions, and higher order chromatin assembly. Small angle neutron scattering will be carried out to further characterize the binding of HMG14 (or 17) to nucleosomes. This program will be extended to include deuterated components of the complex and the study of other constituents of chromatin. The three-dimensional structure of the nucleosome-HMG(14)(2) (or 17) complex and poly(dA-dT) reconstructed nucleosomes will also be studied by X-ray crystallography.